Communications in a Web environment generally involve two different groups of participants. On the one hand there are Web servers, which make available information in the form of displayable pages, and on the other hand there are Web clients (so-called browsers) which display the pages made available by the Web servers. In general a client/server system is therefore organized in such a way that the server does not know its clients. The latter normally only call up the required information from the Web server as a result of user actions. Accordingly, a new Web page is then downloaded to the client, or a new version of the same page is generated. Nowadays, client/servers systems of this type are also increasingly being used in the industrial environment. In this case, the clients are used primarily for displaying information relating, for example to industrial production processes. In a system of this type, new items of information are continuously coming in, via the programmable controllers or diagnostic devices such as sensors, as applicable, and must be displayed to the user of the client, for example a plant operator. These items of information are sent from the programmable controllers or diagnostic devices, as applicable, to the server, and the clients can retrieve the required data from the server. The problem with a client/server system of this type in an industrial environment is that the client is not in general made aware that the values which it is displaying on a page have now changed in the industrial process, so that its display no longer corresponds with the reality. Nowadays, the updating of information is effected by the Web client, after a defined time interval, automatically making a new request for the appropriate information, and refreshing its Web page if necessary. However, the disadvantage with this is that while the Web page is being refreshed it is not displayed to the user of the client, so that for a brief time no information is available to the user for operational purposes. In addition, the inflexible use of a time interval for updating purposes has the consequence that a page is frequently refreshed and requested, even though there is no new information. Superfluous page refreshment and data transfer is thus the rule with this application. Another possible way of supplying the user with up-to-date information consists in establishing a longer term connection between the client and the server. However, this ties up resources on the server, and a special infrastructure must exist on the client. Realizing the updating of items of information in this way is thus relatively expensive.
U.S. Pat. No. 5,713,017 discloses a method by which the updating of data in a fault-tolerant file system is managed with the help of counters.